Virality is central to 21st century marketing, it's hard to imagine an ad being put together without the word viral being used - but it's a very hard thing to get right.

Here's some campaigns that we think were on the money:

1. Mattress Mick

This week Down to Business is coming live from Swords at 11am tomorrow one of our guests is Mattress Mick - Stephen Fry's favourite mattress-man. 

One day I hope to meet Mattress Mick. I think we'll have lots to discuss. Mattresses for example. And prices. pic.twitter.com/1aKChzZXWq

— Stephen Fry (@stephenfry) February 12, 2015

Recently marketing guru Adam Morgan, author of the seminal book, Eating the Big Fish spoke to Newstalk and he said that the Mattress Mick campaign is the best piece of viral marketing that he has seen from an Irish business: 

Speaking with Channel 4's Rude Tube he recalled making his early videos:

"I ad-lib, I don't rehearse, I just stand there and I talk about what comes into my brain - about mattresses."

While this might sound simple, he's managed to build his brand on a tiny budget using just his wits and the power of social media.

2. The Dark Knight

The fundamental issue with most marketing campaigns is that they are trying to get people to care about things that they don't particularly care about - like what brand of toilet paper they use, or which bottle of mineral they should buy.

When you have a product that already excites people, and a savvy, plugged-in marketing team, things can get really interesting - like The Dark Knight's viral marketing.

It blended the film's storyline, with the internet's connectivity and real life events to create an immersive global campaign.

4. Obey

Obey started as a street art campaign by Shepard Fairey, a student at the Rhode Island School of Design art student who took a tabloid image of the WWE (then WWF) wrestler Andre that Giant and started printing stickers of it, and making graffiti stencils.

Initially collaborating with a network of artists, the stickers resonated with a number of subculture groupings, from skaters to hip hop fans who started spreading the stickers in cities around the world.

Fairey cropped tighter on Andre and added 'Obey' to the image, and the street art campaign morphed into a massive commercial urban fashion brand.

As a piece of trivia he also went on to design the iconic Obama 'Hope' poster.

4. Red Bull Space Jump 

This is pretty far away from Mattress Mick - it is probably the most audacious piece of viral marketing ever created.

Red Bull (almost literally) sent someone to space - and then showed them jumping back to earth. Reports from Red Bull's native Austria suggest that €50m was invested in the project - while the global media coverage is estimated to have been worth in excess of €100m.

For Red Bull the name of the game is to associate the brand with excitement and innovation - it has remained tight lipped about the actual sums involved - but the company's owner Dietrich Mateschitz has said that if it was "just a marketing gimmick" is would not have been worth the effort.

5. 2012

2012  was a forgettable film - but it had a memorable marketing campaign. The Guardian was forced to ask if "viral marketing is getting too clever for its own good?" It caused panic is some states in the US - and ended with concerned callers bombarding NASA's phone lines looking to be reassured that the world wasn't actually ending.

It called on viewers to Google "2012" for "The Truth" - this linked them to over 1,000 real websites and 175 real books obsessed with the world ending in 2012.

The film also created a fake organisation called the 'Institute for Human Continuity' - it claimed to be a research group that discovered that there was a 94 percent probability that the world would end in 2012.

It's hard to believe that this could cause War of the World-style panic in the internet age, but NASA has gone on the record about it, saying that they had to deal with so many hysterical calls that it set up a special site to deal with these queries.

NASA also published this video explaining why the world didn't end in 2012.

Down to Business host and entrepreneur Bobby Kerr has some of his own tips to market your business on a shoestring budget.

Bobby and Mattress Mick will both be in Swords for a live broadcast from 11am tomorrow - we still have some free tickets left - to attend, text SWORDS to 53106.